Carbon nanotubes (CNT) have been the subject of intense research since their discovery in 1991. CNT's possess unique properties such as small size, considerable stiffness, and electrical conductivity, which makes them suitable in a wide range of applications, including use as structural materials and in molecular electronics, nanoelectronic components, and field emission displays. Carbon nanotubes may be either multi-walled (MWNTs) or single-walled (SWNTs), and have diameters in the nanometer range.
Little work has been done on the unique chemical properties of carbon nanotubes in solution phase. As an extended conjugated double-bond system with high surface area, carbon nanotubes are expected to stabilize and accumulate charges far better than small molecules. The accumulated charges on a carbon nanotube can be potentially used for redox reactions that are hard to carry out using small molecules.
Methods of manipulating charges on carbon nanotubes by chemical doping and electrochemical control have been reported (Petit, P., et al, Chemical Physics Letters 305, 370-374 (1999); Kavan, L., et al., Chemical Physics Letters 328, 363-368 (2000)). While chemical doping methods and electrochemical processes are conceptually identical to oxidation and reduction, there is a fundamental difference between what has been reported and our method. All the previous experiments were conducted in solid phase with carbon nanotubes mounted on a substrate.
Strano and collaborators have reported a marked sensitivity of the optical transitions to pH in carbon nanotubes dispersed by a surfactant (Strano, M. S. et al. Journal of Physical Chemistry B 107, 6979-6985 (2003)). They further showed that the pH effect was dependent on the presence of O2.
Applicants have shown that dispersed carbon nanotubes can be reversibly and readily oxidized and reduced with common chemicals in solution, thereby allowing the carbon nanotubes to be used as catalysts for chemical reactions and for photoelectrochemical reactions if charge separation is created by light absorption.